Phosphor, method of producing the same, and light emitting apparatus

ABSTRACT

There are provided a phosphor which is a divalent europium-activated oxynitride phosphor substantially represented by General formula (A): Eu a Si b Al c O d N e , a divalent europium-activated oxynitride phosphor substantially represented by General formula (B): MI f Eu g Si h Al k O m N n  or a divalent europium-activated nitride phosphor substantially represented by General formula (C): (MII 1-p Eu p )MIIISiN 3 , having a reflectance of light emission in a longer wavelength region of visible light than a peak wavelength of 95% or larger, and a method of producing such phosphor; a nitride phosphor and an oxynitride phosphor which emit light efficiently and stably by the light having a wavelength ranging from 430 to 480 nm from a semiconductor light emitting device by means of a light emitting apparatus using such phosphor, and a producing method of such phosphor; and a light emitting apparatus having stable characteristics and realizing high efficiency.

This application is a divisional of U.S. application Ser. No.11/944,052, filed Nov. 21, 2007, which claims priority under 35 U.S.C.§119(a) on Japanese Patent Application No. 2006-317524 filed with theJapan Patent Office on Nov. 24, 2006, the entire contents of which arehereby incorporated by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention mainly relates to oxynitride phosphors and nitridephosphors used for a light emitting apparatus, and methods of producingthe same, and further to a light emitting apparatus having a lightconverter using the above phosphor.

Description of the Background Art

A light emitting apparatus having a combination of a semiconductor lightemitting device and a phosphor attracts attention as a next-generationlight emitting apparatus for which low power consumption, compact size,high intensity and high color gamut are expected, and research anddevelopment thereof is actively proceeded. As primary light that isemitted from a light emitting device, usually light from ultraviolet toblue range, more specifically from 380 nm to 480 nm is used. Also, lightconverters adapted to this application using various phosphors have beenproposed.

Also in recent years, an attempt is made for the light emittingapparatus of this type to realize higher brightness by increasing notonly luminous efficiency (brightness) but also input energy. When inputenergy is increased, it is necessary to effectively dissipate the heatof the entire light emitting apparatus including the light converter.For achieving this, development of the entire structure and material oflight emitting apparatus has been proceeded, however, temperature risein a light emitting device and light converter during operation is stillinevitable.

Currently, as a light emitting apparatus exhibiting white light, mainlyused is the combination of a light emitting device that emits blue light(peak wavelength: around 450 nm) and a trivalent cerium-activated (Y,Gd)₃(Al, Ga)₅O₁₂ phosphor or a divalent europium-activated (Sr, Ba,Ca)₂SiO₄ phosphor that is excited by the above blue light and exhibitsyellow light emission.

However, in the trivalent cerium-activated (Y, Gd)₃(Al, Ga)₅O₁₂phosphor, in particular, there is a technical problem that it isimpossible to set input energy at high states because the luminance at100° C. decreases to about 85%, compared to the luminance (brightness)of 100% at 25° C. Therefore, an oxynitride phosphor or a nitridephosphor having excellent temperature characteristics attracts attentionand active development has been made.

However, in such an oxynitride phosphor or nitride phosphor, reflectancein the visible region is not sufficiently high despite the excellentcharacteristics, so that there is a technical problem that it absorbslight emitted from the phosphor itself or the light emitted from otherphosphor. Therefore, in such an oxynitride phosphor or nitride phosphor,improvement in reflectance is urgently needed.

As to such an oxynitride phosphor or nitride phosphor, for example,Japanese Laid-Open Patent Publication No. 2002-363554 (Patentdocument 1) describes α-type SiAlON(SIALON). Specifically, Patentdocument 1 describes Ca-α-SiAlON phosphor activated with varying amountsof Eu²⁺ ion as a representative oxynitride phosphor or nitride phosphor.However, Patent document 1 lacks description about reflectance in thevisible region of phosphor.

In Japanese Laid-Open Patent Publication No. 2006-089547 (Patentdocument 2), β-SiAlON: Eu which is a green phosphor and Ca-α-SiAlON: Euwhich is an yellow phosphor are described. However, Patent document 2also lacks description about the reflectance of phosphor in the visibleregion.

Furthermore, Japanese Laid-Open Patent Publication No. 2004-182780(Patent document 3) describes a nitride phosphor that emits light ofyellow to red regions represented by L_(x)M_(y)N_(((2/3)x+(4/3)y)):R orL_(x)M_(y)O_(z)N_(((2/3)x+(4/3)y-(2/3)z)):R. However, even in Patentdocument 3, there is no description about the reflectance of phosphor inthe visible region.

Japanese Laid-Open Patent Publication No. 10-228868 (Patent document 4)describes provision of a reflection-preventing film of silicon oxide orthe like, on phosphor particles of europium-doped yttrium oxide,manganese-doped zinc silicate, europium-doped barium-magnesium-aluminumoxide or the like. However, Patent document 4 fails to describereflectance of the phosphor itself.

Japanese Laid-Open Patent Publication No. 2004-155907 (Patent document5) discloses an invention relating to a manganese-activated aluminatephosphor having green body color, which is excited by vacuum UV beam andemits green light having a peak wavelength of about 515 nm. A spectralreflectance in a vicinity of the peak wavelength or lower is improved toreduce absorption of light emitted from the phosphor and excitationlight or vacuum UV light and thus increase light emission in luminance.However, the invention does not focus on a reflectance for a wavelengthlonger than the peak wavelength and does not consider absorption oflight emitted from other phosphors, nor does it focus on visible lightexcitation.

SUMMARY OF THE INVENTION

The present invention was made to solve the aforementioned problems, andit is an object of the present invention to provide a nitride phosphorand an oxynitride phosphor which stably emit light with high efficiencyin response to light of 430 to 480 nm from a semiconductor lightemitting device, a method of producing these phosphors, and a lightemitting apparatus realizing high efficiency and stable characteristics.

In order to achieve the above object, present inventors repeatedly madedetailed examination, tests and study about improvement in reflectancein the visible region in specific divalent europium-activated nitrideand oxynitride phosphors, and finally found that nitride and oxynitridephosphors having significantly improved reflectance in the visibleregion can be obtained by optimizing materials and synthetic processesof the phosphors. Specifically, the present invention is as follows.

The present invention provides a divalent europium-activated oxynitridephosphor which is β-type SiAlON substantially represented by Generalformula (A): Eu_(a)Si_(b)Al_(c)O_(d)N_(e), wherein reflectance of lightemission in a longer wavelength region of visible light than a peakwavelength is 95% or larger. In the above General formula (A),0.005≦a≦0.4, b+c=12, and d+e=16 are satisfied.

The present invention provides a divalent europium-activated oxynitridephosphor which is α-type SiAlON substantially represented by Generalformula (B): MI_(f)Eu_(g)Si_(h)Al_(k)O_(m)N_(n), wherein reflectance oflight emission in a longer wavelength region of visible light than apeak wavelength is 95% or larger. In the above General formula (B), MIrepresents at least one kind of element selected from Li, Na, K, Cs, Mg,Ca, Sr and Ba, and 0<f≦3.0, 0.005≦g≦0.4, h+k=12, and m+n=16 aresatisfied. Here, MI in the above General formula (B) is preferably atleast one kind of element selected from Li and Ca.

Also, the present invention provides a divalent europium-activatednitride phosphor substantially represented by General formula (C):(MII_(1-p)Eu_(p))MIIISiN₃, wherein reflectance of light emission in alonger wavelength region of visible light than a peak wavelength is 95%or larger. In the above General formula (C), MII is an alkaline earthmetal element and represents at least one kind of element selected fromMg, Ca, Sr and Ba, and MIII comprises a trivalent metal element, andrepresents at least one kind of element selected from Al, Ga, In, Sc, Y,La, Gd and Lu, and 0.001≦p≦0.05 is satisfied. Here, MIII in the aboveGeneral formula (C) is preferably at least one kind of element selectedfrom Al, Ga and In.

The present invention provides a method of producing a phosphoraccording to the present invention as described above, and also providesa method of producing a phosphor which includes mixing aluminum nitridecovered with fine particle silicon dioxide into materials for thephosphor.

Here, it is preferred that silicon dioxide for covering aluminum nitridehas an average particle diameter of 10 to 200 nm, and occupies 0.01 to15% by weight relative to aluminum nitride.

In the method of producing a phosphor according to the presentinvention, preferably, the materials for phosphor are mixed in an inertatmosphere without using an apparatus for mechanical grinding.

The present invention also provides a light emitting apparatus includinga light emitting device that emits primary light, and a light converterthat absorbs part of the primary light and emits secondary light havinga longer wavelength than that of the primary light, wherein the lightconverter includes at least one selected from a green-based luminousphosphor, an yellow-based luminous phosphor and a red-based luminousphosphor, and the green-based luminous phosphor is a divalenteuropium-activated oxynitride phosphor which is β-type SiAlONsubstantially represented by General formula (A):Eu_(a)Si_(b)Al_(c)O_(d)N_(e), wherein reflectance of light emission in alonger wavelength region of visible light than a peak wavelength is 95%or larger; the yellow-based luminous phosphor is a divalenteuropium-activated oxynitride phosphor which is α-type SiAlONsubstantially represented by General formula (B):MI_(f)Eu_(g)Si_(h)Al_(k)O_(m)N_(n), wherein reflectance of lightemission in a longer wavelength region of visible light than a peakwavelength is 95% or larger; and the red-based luminous phosphor is adivalent europium-activated nitride phosphor which is substantiallyrepresented by General formula (C): (MII_(1-p)Eu_(p))MIIISiN₃, whereinreflectance of light emission in a longer wavelength region of visiblelight than a peak wavelength is 95% or larger. In the above Generalformula (A), 0.005≦a≦0.4, b+c=12, and d+e=16 are satisfied; in the aboveGeneral formula (B), MI represents at least one kind of element selectedfrom Li, Na, K, Cs, Mg, Ca, Sr and Ba, and 0<f≦3.0, 0.005≦g≦0.4, h+k=12,and m+n=16 are satisfied; and in the above General formula (C), MII isan alkaline earth metal element and represents at least one kind ofelement selected from Mg, Ca, Sr and Ba, and MIII comprises a trivalentmetal element, and represents at least one kind of element selected fromAl, Ga, In, Sc, Y, La, Gd and Lu, and 0.001≦p≦0.05 is satisfied.

In the light emitting apparatus according to the present invention, itis preferable to use as the yellow-based luminous phosphor, a divalenteuropium-activated oxynitride phosphor in which MI in General formula(B) is at least one kind of element selected from Li and Ca.

In the light emitting apparatus according to the present invention, itis preferable to use as the red-based luminous phosphor, a divalenteuropium-activated nitride phosphor in which MIII in General formula (C)is at least one kind of element selected from Al, Ga and In.

In the light emitting apparatus according to the present invention, itis preferable that the light emitting device is a gallium nitride-basedsemiconductor device, and primary light from the light emitting devicehas a wavelength ranging from 430 to 480 nm.

The phosphor according to the present invention as described abovestably emits light with high efficiency by the light ranging from 430 to480 nm, and the light emitting apparatus using a light converter havingthe phosphor according to the present invention is able to absorb lightemitted from the light emitting device with high efficiency and offersstable white light with high efficiency.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view schematically showing a light emittingapparatus 1 which is one preferred example of the present invention.

FIG. 2 is a sectional view schematically showing a light emittingapparatus 21 which is other preferred example of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides [1] a divalent europium-activatedoxynitride phosphor which is β-type SiAlON (hereinafter, referred to as“first phosphor”), [2] a divalent europium-activated oxynitride phosphorwhich is α-type SiAlON (hereinafter, referred to as “second phosphor”),and [3] a divalent europium-activated nitride phosphor (hereinafter,referred to as “third phosphor”). In the following, detailed descriptionwill be given for each phosphor.

[1] First Phosphor

The first phosphor according to the present invention is a divalenteuropium-activated oxynitride phosphor which is β-type SiAlON(SIALON)substantially represented by the following General formula (A).Eu_(a)Si_(b)Al_(c)O_(d)N_(e)  General formula (A):

In the above General formula (A), “a” is a value satisfying 0.005≦a≦0.4,preferably 0.01≦a≦0.2. When the value of “a” is less than 0.005, aproblem arises that sufficient brightness is not obtained, whereas whenthe value of “a” is more than 0.4, a problem arises that brightnesslargely drops due to concentration quenching or the like. In the aboveGeneral formula (A), b+c=12, and d+e=16 are satisfied.

Concrete examples of such a divalent europium-activated oxynitridephosphor which is β-type SiAlON include, but are obviously not limitedto, Eu_(0.03)Si_(11.63)Al_(0.37)O_(0.03)N_(15.97),Eu_(0.05)Si_(11.50)Al_(0.50)O_(0.05)N_(15.95),Eu_(0.10)Si_(11.01)Al_(0.99)O_(0.20)N_(15.80),Eu_(0.30)Si_(9.80)Al_(2.20)O_(0.30)N_(15.70),Eu_(0.005)Si_(11.70)Al_(0.30)O_(0.03)N_(15.97),Eu_(0.01)Si_(11.60)Al_(0.40)O_(0.01)N_(15.99),Eu_(0.15)Si_(10.00)Al_(2.00)O_(0.20)N_(15.80) and so on.

In the first phosphor according to the present invention, reflectance oflight emission in a longer wavelength region of visible light than apeak wavelength is 95% or larger (preferably 97% or larger). Whenreflectance of light emission in a longer wavelength region of visiblelight than the peak wavelength is less than 95%, output of white-basedcolor drawn outside significantly decreases because visible lightemitted from the phosphor is absorbed. The reflectance is calculated by(100−absorptance) from absorptance in a longer wavelength region ofvisible light than the peak wavelength that is measured, for example, byMCPD7000 manufactured by OTSUKA ELECTRONICS CO., LTD.

As to the first phosphor according to the present invention, itsparticle diameter is not particularly limited, however, an averageparticle diameter measured by Blaine method falls preferably in therange of 2 to 8 μm, and more preferably in the range of 3 to 6 μm. Whenthe average particle diameter of the first phosphor is less than 2 μm,crystal growth is insufficient, and brightness in a light emittingapparatus using the same tends to greatly decrease. On the other hand,when the average particle diameter of the first phosphor is larger than8 μm, bulk particles that have grown abnormally are likely to begenerated, so that the practicability is poor.

[2] Second Phosphor

The second phosphor according to the present invention is a divalenteuropium-activated oxynitride phosphor which is α-type SiAlONsubstantially represented by the following General formula (B).MI_(f)Eu_(g)Si_(h)Al_(k)O_(m)N_(n)  General formula (B):

In the above General formula (B), MI represents at least one kind ofelement selected from Li, Na, K, Cs, Mg, Ca, Sr and Ba. Among these, itis more preferred that MI is at least one kind selected from Li and Cabecause a light emitting apparatus that emits brighter light isobtained.

In the above General formula (B), the value of “f” satisfies 0<f≦3.0,and more preferably 0.1≦f≦2.0. When the value of “f” is 0 (that is, MIis not contained), and when the value of “f” is more than 3.0, it isimpossible to achieve stable solid solution in a lattice, so that atrouble arises that sufficient brightness is not obtained.

In the above General formula (B), the value of “g” satisfies0.005≦g≦0.4, and preferably 0.02≦g≦0.2. When the value of “g” is lessthan 0.005, a trouble arises that sufficient brightness is not obtained,while when the value of “g” is more than 0.4, a trouble that brightnesssignificantly decreases due to concentration quenching or the likearises.

In the above General formula (B), h+k=12, and m+n=16 are satisfied.

Concrete examples of the divalent europium-activated oxynitride phosphorwhich is α-type SiAlON as described above include, but are obviously notlimited to, Ca_(0.6)Eu_(0.05)Si_(10.52)Al_(1.48)O_(0.88)N_(15.12),Ca_(0.2)Eu_(0.01)Si_(10.10)Al_(1.90)O_(0.80)N_(15.20),Ca_(1.0)Eu_(0.06)Si_(10.72)Al_(1.28)O_(1.38)N_(14.62),Ca_(0.3)Eu_(0.10)Si_(10.20)Al_(1.80)O_(0.40)N_(15.60),Ca_(0.4)Mg_(0.1)Eu_(0.03)Si_(10.00)Al_(2.00)O_(1.10)N_(14.90),Ca_(0.75)Eu_(0.01)Si_(9.75)Al_(2.25)O_(0.76)N_(15.24),Ca_(0.50)Li_(0.10)Eu_(0.01)Si_(11.50)Al_(0.50)O_(0.20)N_(15.80), andCa_(1.00)Sr_(0.10)Eu_(0.20)Si_(10.00)Al_(2.00)O_(0.30)N_(15.70).

In the second phosphor according to the present invention, reflectanceof light emission in a longer wavelength region of visible light than apeak wavelength is 95% or larger (preferably 97% or larger) for the samereason as previously described in relation to the first phosphoraccording to the present invention. The reflectance of light emission ina longer wavelength region of visible light than a peak wavelength inthe second phosphor according to the present invention also representsthe value measured in the same manner as described for the case of thefirst phosphor according to the present invention.

As to the second phosphor according to the present invention, itsparticle diameter is not particularly limited, however, the averageparticle diameter measured by Blaine method falls preferably in therange of 2 to 8 μm, and more preferably in the range of 3 to 6 μm. Whenthe average particle diameter of the second phosphor is less than 2 μm,crystal growth is insufficient, and brightness in a light emittingapparatus using the same tends to greatly decrease. On the other hand,when the average particle diameter of the second phosphor is larger than8 μm, bulk particles that have grown abnormally are likely to begenerated, so that the practicability is poor.

[3] Third Phosphor

The third phosphor according to the present invention is a divalenteuropium-activated nitride phosphor which is substantially representedby the following General formula (C).(MII_(1-p)Eu_(p))MIIISiN₃  General formula (C):

In the above General formula (C), MII is an alkaline earth metal, andrepresents at least one kind of element selected from Mg, Ca, Sr and Ba.

In General formula (C), MIII is a trivalent metal element, andrepresents at least one kind of element selected from Al, Ga, In, Sc, Y,La, Gd and Lu. Among these, MIII is preferably at least one kind ofelement selected from Al, Ga and In because more efficient emission ofred-based light is possible.

In the above General formula (C), the value of “p” satisfies0.001≦p≦0.05, and preferably 0.005≦p≦0.02. When the value of “p” is lessthan 0.001, a trouble that sufficient brightness is not obtained arises,while when the value of “p” is more than 0.05, a trouble that brightnesssignificantly decreases due to concentration quenching or the likearises.

Concrete examples of such a divalent europium-activated nitride phosphorinclude, but are obviously not limited to, Ca_(0.990)Eu_(0.010)SiAlN₃,(Ca_(0.97)Mg_(0.02)Eu_(0.01))(Al_(0.99)Ga_(0.001))SiN₃,(Ca_(0.98)Eu_(0.02))AlSiN₃,(Ca_(0.97)Sr_(0.01)Eu_(0.02))(Al_(0.98)In_(0.02))SiN₃,(Ca_(0.999)Eu_(0.001))AlSiN₃, (Ca_(0.895)Mg_(0.100)Eu_(0.005))AlSiN₃,(Ca_(0.79)Sr_(0.20)Eu_(0.01))AlSiN₃, and(Ca_(0.98)Eu_(0.02))(Al_(0.95)Ga_(0.05))SiN₃.

In the third phosphor according to the present invention, reflectance oflight emission in a longer wavelength region of visible light than apeak wavelength is 95% or larger (preferably 97% or larger) for the samereason as previously described in relation to the first phosphoraccording to the present invention. The reflectance of light emission ina longer wavelength region of visible light than a peak wavelength inthe third phosphor according to the present invention is also determinedin the same manner as described for the case of the first phosphoraccording to the present invention.

As to the third phosphor according to the present invention, itsparticle diameter is not particularly limited, however, the averageparticle diameter measured by Blaine method falls preferably in therange of 3 to 10 μm, and more preferably in the range of 4 to 7 μm. Whenthe average particle diameter of the third phosphor is less than 3 μm,crystal growth is insufficient, and brightness in a light emittingapparatus using the same tends to greatly decrease. On the other hand,when the average particle diameter of the third phosphor is larger than10 μm, bulk particles that have grown abnormally are likely to begenerated, so that the practicability is poor.

Production methods of the first to third phosphors according to thepresent invention as described above are not particularly limitedinsofar as they are produced so that they have the aforementionedreflectances of light emission in a longer wavelength region of visiblelight than a peak wavelength, respectively. In the present invention,also provided is a method capable of suitably producing the first tothird phosphors according to the present invention as described above.That is, the present method of producing a phosphor is characterized bymixing aluminum nitride (AlN) covered with fine particle silicon dioxide(SiO₂) into materials for the phosphor.

Fine particle silicon dioxide covering aluminum nitride used in themethod of producing a phosphor according to the present invention has anaverage particle diameter preferably ranging from 10 to 200 nm, and morepreferably ranging from 20 to 80 nm. When the average particle diameterof silicon dioxide is less than 10 nm, it could be impossible to form auniform covering layer, and when the average particle diameter ofsilicon dioxide is more than 200 nm, it could be impossible to keep thechemical stability of aluminum nitride covered with the same. Theaverage particle diameter of silicon dioxide may be determined bymeasuring specific surface area by using an appropriate apparatus knownin the art, and determining an average particle diameter on theassumption that the particle is spherical, or may be calculated from itsimage using an SEM.

Covering amount by silicon dioxide is preferably in the range of 0.01 to15% by weight, and more preferably in the range of 0.1 to 5% by weightrelative to aluminum nitride. When the covering amount by silicondioxide is less than 0.01% by weight relative to aluminum nitride, ittends to become difficult to form a uniform covering layer, and when thecovering amount by silicon dioxide is more than 15% by weight relativeto aluminum nitride, brightness of the phosphor tends to decreasesignificantly. The covering amount of silicon dioxide may be determinedby quantitative analysis using, for example, ICP (inductively-coupledhigh-frequency plasma) spectrometry.

In the method of producing a phosphor according to the presentinvention, materials for the phosphor may be mixed by using an apparatusfor mechanical grinding such as a vibration mill, however, from theviewpoint of realizing stable mixing of materials for the phosphor whilekeeping chemical stability of aluminum nitride, and preventingoxidization of materials for a phosphor such as Si₃N₄, it is preferredto mix the materials for the phosphor in an inert atmosphere withoutusing such an apparatus for mechanical grinding. As the inertatmosphere, nitrogen, argon and the like atmosphere may be used withoutany limitation.

The present invention also provides light emitting apparatuses using thefirst to third phosphors according to the present invention as describedabove. To be more specific, a light emitting apparatus according to thepresent invention basically has a light emitting device that emitsprimary light, and a light converter that absorbs part of the primarylight and emits secondary light having a wavelength longer than that ofthe primary light, and the light converter includes at least one offirst to third phosphors: the aforementioned first phosphor as agreen-based luminous phosphor, the aforementioned second phosphor as anyellow-based luminous phosphor, and the aforementioned third phosphor asa red-based luminous phosphor. Here, FIG. 1 is a sectional viewschematically showing a light emitting apparatus 1 which is onepreferred example of the present invention. FIG. 2 is a sectional viewschematically showing a light emitting apparatus 21 which is anotherpreferred example of the present invention. Light emitting device 1which is the example shown in FIG. 1 basically has a light emittingdevice 2 and a light converter 3, and light converter 3 includes theaforementioned first phosphor as a green-based luminous phosphor 4, andthe aforementioned third phosphor as a red-based luminous phosphor 5.Light emitting device 21 which is the example shown in FIG. 2 basicallyhas a light emitting device 2 and a light converter 22, and lightconverter 22 includes the aforementioned second phosphor as anyellow-based luminous phosphor 23. As described above, a light emittingapparatus according to the present invention is preferably realized sothat the light converter includes (1) a green-based luminous phosphor(the aforementioned first phosphor) and a red-based luminous phosphor(the aforementioned third phosphor) (example shown in FIG. 1) or (2) anyellow-based luminous phosphor (second phosphor) (example shown in FIG.2).

All of the first to third phosphors used in light emitting apparatuses1, 21 according to the present invention have a reflectance of lightemission in a longer wavelength region of visible light than a peakwavelength of 95% or larger (preferably 97% or larger). Such a phosphorstably emits light with high efficiency by light ranging from 430 to 480nm, and hence, in light emitting apparatuses 1, 21 according to thepresent invention using such first to third phosphors, it is possible toobtain stable white light with high efficiency as a result of efficientabsorption of light from light emitting device 2.

Further, since the first to third phosphors according to the presentinvention used in light emitting apparatuses 1, 21 according to thepresent invention are ceramic materials which are high in heatresistance and small in coefficient of heat expansion, variation in bandgap is small. In light emitting apparatuses 1, 21 according to thepresent invention, by using such first to third phosphors,advantageously a light emitting apparatus in which decrease inefficiency of fluorescent emission with respect to temperature is smalland temperature characteristics are dramatically improved compared toconventional one can be realized.

In light emitting apparatus 1 of the example shown in FIG. 1, since thephosphor according to the present invention used as green-based luminousphosphor 4 has narrow half width of the emission spectrum, theaforementioned temperature characteristic is excellent, and color gamut(NTSC ratio) is excellent. Therefore, such light emitting apparatus 1according to the present invention efficiently absorbs light emittedfrom light emitting device 2 and emits white light with high efficiency,offers excellent white color with very good color gamut (NTSC ratio),and offers white color having an excellent general color rendering index(Ra), so that it is desirable for generic illumination. As describedabove, light emitting apparatus 1 according to the present invention ispreferably realized as a white LED, and among others, use as a lightsource for backlighting of an LCD is particularly suitable.

In light emitting apparatus 21 of the example shown in FIG. 2, as toyellow-based luminous phosphor (second phosphor of the presentinvention) 23 contained in light converter 22, MI in General formula (B)is preferably at least one kind of element selected from Li and Ca forthe same reason as described above.

In light emitting apparatus 1 of the example shown in FIG. 1, as tored-based luminous phosphor (third phosphor of the present invention) 5contained in light converter 3, MIII in General formula (C) ispreferably at least one kind of element selected from Al, Ga and In.

In light emitting apparatus 1 according to the present invention whichis the example shown in FIG. 1, light converter 3 can be produced bykneading a green-based luminous phosphor and a red-based luminousphosphor while using, e.g., a thermosetting-type silicone sealing memberas a medium, and molding by sealing light emitting device 2. Blendingratio between the green-based luminous phosphor and the red-basedluminous phosphor is not particularly limited, however, for obtainingwhite light of desired chromaticity, the case of producing a lightconverter is exemplified wherein the green-based luminous phosphor is1/10 of medium by weight ratio, and the red-based luminous phosphor is1/50 of medium by weight ratio.

Light converters 3, 22 in light emitting apparatuses 1, 21 according tothe present invention contain at least any one selected from green-basedluminous phosphor 4, yellow-based luminous phosphor 23 and red-basedluminous phosphor 5 as described above, and a medium 6 thereof is notparticularly limited insofar as part of the primary light emitted fromlight emitting device 2 is absorbed and the secondary light having awavelength longer than that of the primary light is emitted. As medium6, for example, transparent resins such as epoxy resin, silicone resinand urea resin can be used, without limited thereto.

Of course, light converters may further contain additives such as SiO₂,TiO₂, ZrO₂, Al₂O₃, Y₂O₃ and the like as appropriate in addition to theaforementioned phosphor and medium as far as the effect of the presentinvention is not inhibited.

As light emitting device 2 used in light emitting apparatuses 1, 21according to the present invention, gallium nitride (GaN) semiconductorcan be preferably used from the viewpoint of efficiency. From theviewpoint of making light emitting apparatus 1 according to the presentinvention emit light efficiently, light emitting device 2 used in lightemitting apparatuses 1, 21 according to the present invention preferablyemits primary light having a peak wavelength ranging from 430 to 480 nm,and more preferably emits primary light having a peak wavelength rangingfrom 440 to 470 nm. When the peak wavelength of primary light emittedfrom light emitting device 2 is less than 430 nm, color renderingproperty is impaired, and thus is impractical. When the peak wavelengthis more than 480 nm, brightness in white color decreases, and thepracticality tends to be lost.

The light converter in the light emitting apparatus according to thepresent invention can be produced by dispersing the aforementionedgreen-based luminous phosphor 4, yellow-based luminous phosphor 23 andred-based luminous phosphor 5 in an appropriate resin, and molding underappropriate conditions, and the producing method is not particularlylimited.

In the following, the present invention will be described in more detailby way of examples and comparative examples, however it is to be notedthat the present invention is not limited to such examples.

Example 1

191.64 g of silicon nitride (Si₃N₄) powder, 6.75 g of aluminum nitride(AlN) powder covered with 2.0% by weight of silicon dioxide (SiO₂)having an average particle diameter of 24 nm, and 1.62 g of europiumoxide (Eu₂O₃) powder were weighed, and introduced into a V-shaped mixerin a glove box the entirety of which is substituted with nitrogen, andmixed for twenty minutes. The obtained mixture was put into a crucibleof boron nitride and calcined for eight hours at 2000° C. in nitrogenatmosphere at 10 atm. The obtained calcined substance was ground by aball mill or the like. The ground powder was put into a crucible ofboron nitride, and calcined for ten hours at 1700° C. in nitrogenatmosphere at 5 atm. The obtained calcined substance was ground by aball mill or the like. After grinding, 1 L of pure water was put into a1 L-beaker, followed by the calcined substance, and stirred. Afterstirring for a predetermined time, the stirring was stopped and thereaction was kept still to remove fine particle components that haveoccurred during the grinding. This cleaning operation was repeated toremove most of the fine particle components. Thereafter, filtration anddrying (110° C., 16 hours) were conducted. The obtained phosphor was3-type SiAlON represented by Eu_(0.03)Si_(11.63)Al_(0.37)O_(0.03)N_(15.97).

Comparative Example 1

The method similar to that of Example 1 was conducted except thataluminum nitride (AlN) powder not covered with silicon dioxide (SiO₂)was used, and as a mixture of materials, a mixture obtained by adding ahigher hydrocarbon solvent represented by n-C_(n)H_(2n+2) in mixing wasused. The obtained phosphor was β-type SiAlON represented byEu_(0.03)Si_(11.63)Al_(10.37)O_(0.03)N_(15.97).

Example 2

118.60 g of silicon nitride (Si₃N₄) powder, 16.46 g of aluminum nitride(AlN) powder covered with 10.0% by weight of silicon dioxide (SiO₂)having an average particle diameter of 100 nm, 2.12 g of europium oxide(Eu₂O₃) powder, and 14.47 g of calcium carbonate (CaCO₃) powder wereweighed, introduced into a V-shaped mixer in a glove box the entirety ofwhich is substituted with nitrogen, and mixed for twenty minutes. Theobtained mixture was put into a crucible of boron nitride and calcinedfor twelve hours at 1700° C. in nitrogen atmosphere at 10 atm. Theobtained calcined substance was ground by a ball mill or the like. Aftergrinding, 1 L of pure water was put into a 1 L-beaker, followed by thecalcined substance, and stirred. After stirring for a predeterminedtime, the stirring was stopped and the reaction was kept still to removefine particle components that have occurred during the grinding. Thiscleaning operation was repeated to remove most of the fine particlecomponents. Thereafter, filtration and drying (110° C., 16 hours) wereconducted. The obtained phosphor was α-type SiAlON represented byCa_(0.6)Eu_(0.05)Si_(10.52)Al_(1.48)O_(0.88)N_(15.12).

Comparative Example 2

α-type SiAlON represented byCa_(0.6)Eu_(0.05)Si_(10.50)Al_(1.50)O_(0.70)N_(15.30) was obtained inthe same manner as in Example 2 except that aluminum nitride (AlN)powder that is not covered with silicon dioxide (SiO₂) was used, and amixture that was mixed by using a ball mill was used as the mixture ofmaterials.

Example 3

56.54 g of calcium nitride (Ca₃N₂) powder, 47.38 g of aluminum nitride(AlN) powder covered with 0.1% by weight of silicon dioxide (SiO₂)having an average particle diameter of 45 nm, 54.05 g of silicon nitride(Si₃N₄) powder, and 2.03 g of europium oxide (Eu₂O₃) powder wereweighed, and introduced into a V-shaped mixer in a glove box theentirety of which is substituted with nitrogen, and mixed for twentyminutes. The obtained mixture was put into a crucible of boron nitrideand calcined for five hours at 1500° C. in nitrogen atmosphere. Theobtained calcined substance was ground by a ball mill or the like. Aftergrinding, 1 L of pure water was put into a 1 L-beaker, followed by thecalcined substance, and stirred. After stirring for a predeterminedtime, the stirring was stopped and the reaction was kept still to removefine particle components that have occurred during the grinding. Thiscleaning operation was repeated to remove most of the fine particlecomponents. Thereafter, filtration and drying (110° C., 16 hours) wereconducted. The obtained phosphor was a nitride phosphor represented byCa_(0.990)Eu_(0.010)SiAlN₃.

Comparative Example 3

A phosphor was produced in the same manner as in Example 3 except thataluminum nitride (AlN) powder that is not covered with silicon dioxide(SiO₂) was used, and a mixture that was mixed by using a ball mill wasused as the mixture of materials.

(Evaluation Test 1)

Using the phosphors obtained in Examples 1 to 3, and Comparativeexamples 1 to 3, absorptance in a longer wavelength region than a peakwavelength was measured with the use of MCPD7000 manufactured by OTSUKAELECTRONICS CO., LTD., and reflectance was calculated from theabsorptance. Phosphors of Example 1 and Comparative example 1 had peakwavelengths around 540 nm, and reflectance in a longer wavelength regionthan around 540 nm was 97.3% for the phosphor in Example 1, and 85.2%for the phosphor in Comparative example 1. Phosphors of Example 2 andComparative example 2 had peak wavelengths around 585 nm, andreflectance in a longer wavelength region than around 585 nm was 97.0%for the phosphor in Example 2, and 84.1% for the phosphor in Comparativeexample 2. Phosphors of Example 3 and Comparative example 3 had peakwavelengths around 645 nm, and reflectance in a longer wavelength regionthan around 645 nm was 97.6% for the phosphor in Example 3, and 86.0%for the phosphor in Comparative example 3. Reflectances measured forExamples 1 to 3 and Comparative examples 1 to 3 are shown in Table 1

TABLE 1 REFLECTANCE (%) EXAMPLE 1 97.3 COMPARATIVE EXAMPLE 1 85.2EXAMPLE 2 97.0 COMPARATIVE EXAMPLE 2 84.1 EXAMPLE 3 97.6 COMPARATIVEEXAMPLE 3 86.0

Table 1 demonstrates that the phosphors according to the presentinvention exhibit better reflectances in comparison with theconventional ones.

Examples 4 to 14 Comparative Examples 4 to 14

Each phosphor shown in Table 2 was produced in a similar manner asdescribed in Examples 1 to 3 and subjected to an evaluation test. InTable 2, the average particle diameter (nm) and covering amount (% byweight) of silicon dioxide (SiO₂) that covers aluminum nitride (AlN)powder are shown together.

TABLE 2 COVERING SIZE AMOUNT REFLECTANCE COMPOSITION (nm) (WT. %) (%)EXAMPLE 4 Eu_(0.05)Si_(11.50)Al_(0.50)O_(0.05)N_(15.95) (β-type SiAlON)70 5.0 97.9 COMPARATIVE Eu_(0.05)Si_(11.50)Al_(0.50)O_(0.05)N_(15.95)(β-type SiAlON) — — 84.3 EXAMPLE 4 EXAMPLE 5Eu_(0.10)Si_(11.01)Al_(0.99)O_(0.20)N_(15.80) (β-type SiAlON) 15 15.0 97.7 COMPARATIVE Eu_(0.10)Si_(11.00)Al_(1.00)O_(0.10)N_(15.90) (β-typeSiAlON) — — 84.0 EXAMPLE 5 EXAMPLE 6Eu_(0.30)Si_(9.80)Al_(2.20)O_(0.30)N_(15.70) (β-type SiAlON) 200  1.097.0 COMPARATIVE Eu_(0.30)Si_(9.80)Al_(2.20)O_(0.30)N_(15.70) (β-typeSiAlON) — — 85.3 EXAMPLE 6 EXAMPLE 7Ca_(0.2)Eu_(0.01)Si_(10.10)Al_(1.90)O_(0.80)N_(15.20) (α-type SiAlON) 63 0.01 96.9 COMPARATIVECa_(0.2)Eu_(0.01)Si_(10.10)Al_(1.90)O_(0.80)N_(15.20) (α-type SiAlON) —— 85.5 EXAMPLE 7 EXAMPLE 8Ca_(1.0)Eu_(0.06)Si_(10.72)Al_(1.28)O_(1.38)N_(14.62) (α-type SiAlON) 518.0 97.8 COMPARATIVECa_(1.0)Eu_(0.06)Si_(10.70)Al_(1.30)O_(1.20)N_(14.80) (α-type SiAlON) —— 84.9 EXAMPLE 8 EXAMPLE 9Ca_(0.3)Eu_(0.10)Si_(10.20)Al_(1.80)O_(0.40)N_(15.60) (α-type SiAlON) 333.0 97.5 COMPARATIVECa_(0.3)Eu_(0.10)Si_(10.20)Al_(1.80)O_(0.40)N_(15.60) (α-type SiAlON) —— 85.1 EXAMPLE 9 EXAMPLE 10Ca_(0.4)Mg_(0.1)Eu_(0.03)Si_(10.00)Al_(2.00)O_(1.10)N_(14.90) (α-type 850.5 97.8 SiAlON) COMPARATIVECa_(0.4)Mg_(0.1)Eu_(0.03)Si_(10.00)Al_(2.00)O_(1.10)N_(14.90) (α-type —— 84.8 EXAMPLE 10 SiAlON) EXAMPLE 11 (Ca_(0.97)Mg_(0.02)Eu_(0.01))(Al_(0.99)Ga_(0.01))SiN₃ 12 0.3 97.9 COMPARATIVE(Ca_(0.97)Mg_(0.02)Eu_(0.01)) (Al_(0.99)Ga_(0.01))SiN₃ — — 85.1 EXAMPLE11 EXAMPLE 12 (Ca_(0.98)Eu_(0.02))AlSiN₃ 75 1.0 97.2 COMPARATIVE(Ca_(0.98)Eu_(0.02))AlSiN₃ — — 84.5 EXAMPLE 12 EXAMPLE 13(Ca_(0.97)Sr_(0.01)Eu_(0.02)) (Al_(0.98)In_(0.02))SiN₃ 39 0.6 97.5COMPARATIVE (Ca_(0.97)Sr_(0.01)Eu_(0.02)) (Al_(0.98)In_(0.02))SiN₃ — —84.9 EXAMPLE 13 EXAMPLE 14 (Ca_(0.999)Eu_(0.001))AlSiN₃ 25  0.01 97.8COMPARATIVE (Ca_(0.999)Eu_(0.001))AlSiN₃ — — 85.0 EXAMPLE 14

Table 2 demonstrates that the phosphors according to the presentinvention exhibit better reflectances in comparison with theconventional ones.

Example 15

As a light emitting device, gallium nitride (GaN) semiconductor having apeak wavelength at 440 nm was used. As a light converter, the one havingcomposition Ca_(0.6)Eu_(0.05)Si_(10.52)Al_(1.48)O_(0.88)N_(15.12)(α-type SiAlON)(Example 2) having a peak wavelength around 585 nm andreflectance in a longer wavelength region than around 585 nm of 97.0%was used as an yellow-based luminous phosphor. This phosphor wasdispersed in a predetermined silicone resin to form a light converter,and a light emitting apparatus was produced.

Comparative Example 15

A light emitting apparatus was produced in a similar manner as inExample 15 except that an yellow-based luminous phosphor which hasreflectance in a longer wavelength region than around 585 nm of 84.1%and is represented byCa_(0.6)Eu_(0.05)Si_(10.50)Al_(1.50)O_(0.70)N_(15.30) (α-typeSiAlON)(Comparative example 2) was used as the light converter.

(Evaluation Test 2)

The light emitting apparatuses produced in Example 15, and Comparativeexample 15 were operated with a forward current of 20 mA, and theircharacteristics (luminosity) were evaluated. The results are shown inTable 3.

TABLE 3 BRIGHTNESS Tc-duv (RELATIVE VALUE) EXAMPLE 15 3000K + 0.003100.0% COMPARATIVE 3000K + 0.003 86.7% EXAMPLE 15

Table 3 demonstrates that the light emitting apparatus according to thepresent invention exhibits better stability of characteristics,particularly stability in luminance characteristic, in comparison withthe conventional one.

Examples 16 to 18 Comparative Examples 16 to 18

A light emitting apparatus was produced in a similar manner as inExample 15 using a combination of light emitting device and phosphor asshown in Table 4, and subjected to an evaluation test.

TABLE 4 LIGHT BRIGHTNESS EMITTING (RELATIVE DEVICE FLUORESCENT SUBSTANCETc-duv VALUE) EXAMPLE 16 430 nm EXAMPLE 7 2900K + 0.003 100.0%COMPARATIVE 430 nm COMPARATIVE EXAMPLE 7 2900K + 0.003 88.2% EXAMPLE 16EXAMPLE 17 470 nm EXAMPLE 1 + EXAMPLE 11 6700K + 0.003 100.0%COMPARATIVE 470 nm COMPARATIVE EXAMPLE 1 + 6700K + 0.003 86.7% EXAMPLE17 COMPARATIVE EXAMPLE 11 EXAMPLE 18 480 nm EXAMPLE 5 + EXAMPLE 128700K + 0.001 100.0% COMPARATIVE 480 nm COMPARATIVE EXAMPLE 5 + 8700K +0.001 86.0% EXAMPLE 18 COMPARATIVE EXAMPLE 12

Table 4 demonstrates that the light emitting apparatus according to thepresent invention exhibits better stability of characteristics,particularly stability in luminance characteristic, in comparison withthe conventional one.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the scopeof the present invention being interpreted by the terms of the appendedclaims.

What is claimed is:
 1. A light converter comprising: (i) a red-basedluminous phosphor having a reflectance of 95% or larger in a region ofvisible light having wavelengths longer than a peak wavelength of thered-based luminous phosphor and comprising a divalent europium-activatednitride phosphor substantially represented by the formula:(MII_(1-p)Eu_(p))MIIIS_(i)N₃, wherein MII comprises at least onealkaline earth metal element selected from the group consisting of Mg,Ca, Sr and Ba, MIII comprises at least one trivalent metal elementselected from the group consisting of Al, Ga, In, Sc, Y, La, Gd and Lu,and 0.005≦p≦0.02; and (ii) a green-based luminous phosphor having areflectance of 95% or larger in a region of visible light havingwavelengths longer than a peak wave length of the green-based luminousphosphor and comprising a divalent europium-activated oxynitridephosphor comprising a β-type SiAlON substantially represented by theformula: Eu_(a)Si_(b)Al_(c)O_(d)N_(e), wherein 0.005≦a≦0.4, b+c=12, andd+e=16.
 2. The light converter according to claim 1, wherein MIII is atleast one element selected from the group consisting of Al, Ga and In.3. A light emitting apparatus comprising: a light emitting device thatemits a primary light; and a light converter that absorbs part of saidprimary light and emits secondary light having a longer wavelength thanthat of said primary light, said light converter comprising a red-basedluminous phosphor and a green-based luminous phosphor, wherein saidred-based luminous phosphor has a reflectance of 95% or larger in alonger wavelength region of visible light than a peak wavelength of thered-based luminous phosphor and comprises a divalent europium-activatednitride phosphor substantially represented by the formula:(MII_(1-p)Eu_(p))MIIIS_(i)N₃, wherein MII comprises at least onealkaline earth metal selected from the group consisting of Mg, Ca, Srand Ba, MIII comprises at least one trivalent metal element selectedfrom the group consisting of Al, Ga, In, Sc, Y, La, Gd and Lu, and0.005≦p≦0.02, and wherein said green-based luminous phosphor has areflectance of 95% or larger in a longer wavelength region of visiblelight than a peak wavelength of the green-based luminous phosphor andcomprises a β-type SiAlON substantially represented by the formula:Eu_(a)Si_(b)Al_(c)O_(d)N_(e), in which 0.005≦a≦0.4, b+c=12, and d+e=16.4. The light emitting apparatus according to claim 3, wherein MIII is atleast one element selected from the group consisting of Al, Ga and In.5. The light emitting apparatus according to claim 3, wherein said lightemitting device is a gallium nitride-based semiconductor device, andprimary light from the light-emitting device has a wavelength rangingfrom 430 to 480 nm.